Download Chapter 2 - Net Start Class

Chapter 2
Section 1 Part B
Average Speed
Average Speed describes speed of motion when speed is changing. Average Speed
is the distance traveled divided by the time of travel. It can be calculated using the
relationship among speed distance and time.
If Mr. Van Fleet rides his bicycle to work, and he lives 10 miles away, how fast did
he travel if it takes him ¼ hour or .25 hour?
Formula: s=d/t
Distance = 10 miles, time = .25 hour
Speed = 10/.25 = 40 mph
The 40 mph would be the average speed since we don’t know if he stopped or
slowed down on the road.
Instantaneous Speed
A speedometer shows how fast a car is going at one point in time or
at one instant. The speed shown on a speedometer is the
instantaneous speed. Instantaneous speed is the speed at a point in
time.
Graphing Motion
A distance-time graph makes it possible to display the motion of an
object over a period of time.
The straight red line represents the motion at a constant
speed.
This line represents the motion of something that doesn’t
move at a constant speed. Say that a car starts off moving at a constant speed but
stops at a stop sign. Then it accelerates before it has to stop again. Notice that
when you are not moving, you lay “flat” on the same line, but when you are moving
you are making a slope.
Plotting a Distance –Time Graph
Plotting a distance-time graph is simple. The distance is plotted
on the vertical axis and the time on the horizontal axis (x-axis).
Q: which of the following graphs is the runner running the fastest?
Hint:
which as the greatest slope?
Which of the following graphs indicates that one of runners started 10 yards ahead of the other?
Velocity
Say an enormous hurricane is coming towards you.
you hear that the storm is traveling 20 km/h, and is
located 100 km east of your location. Should you be worried?
Unfortunately, you don’t have enough information to figure out the
answer. Knowing only the speed of the storm isn’t much help. You need
to know the velocity as well.
Velocity – includes the speed of an object and the direction of its motion.
The speed of the passengers is the same,
but their velocities are different because the passengers are moving in
different directions.
Because velocity depends on direction as well as
speed, the velocity of an object can change even
if the speed of the object remains constant.
Example:
a car traveling around in a circle.
If the car has a constant speed of 100 km/h and
is going around an oval track, the velocity
changes because the direction of the car’s motion
is changing constantly.
Can you think of anything that is moving so
slowly you cannot detect it?
The Earth’s crust is your answer.
Russia, here we come!
Look out